Doughtnut-shaped hollow core body, bidirectional hollow core slab using the same, and construction method thereof

ABSTRACT

The present invention relates to a lightweight bidirectional hollow core slab, and a doughnut-shaped hollow core body which may be advantageously used in the construction of a bidirectional hollow core slab. The doughnut-shaped hollow core body according to the present invention includes an outer case formed in a generally doughnut shape, wherein a hollow portion with a circular section is formed in the center thereof and corners are rounded with curved surfaces. The bidirectional hollow core slab according to the present invention is made by stably locating the doughnut-shaped hollow core bodies in concrete in such a manner that the doughnut-shaped hollow core body is restrained and mounted in steel bar cages or on the upper and lower steel bars.

TECHNICAL FIELD

The present invention relates to a lightweight bidirectional hollow coreslab that is made by arranging a plurality of hollow core bodies betweenupper and lower steel bars in a form of a matrix in horizontal andvertical directions thereof and by burying the hollow core bodies intoconcrete, thereby providing bidirectional resistance characteristics.More particularly, the present invention relates to a doughnut-shapedhollow core body advantageously used for a bidirectional hollow coreslab, the bidirectional hollow core body using the doughnut-shapedhollow core body, and a construction method of the bidirectional hollowcore body.

BACKGROUND OF INVENTION

A hollow core slab has hollow cores formed on the center thereof, whichprovide more excellent sectional performance than the self weight andare advantageous in the reduction of the noise between floors.

In view of the light weight of the slab, one of slab systems used forcurrent buildings is one-way hollow core slab. Most of the slabs ofbuildings such as apartment houses show bidirectional (two-way)movements, thereby making it impossible to apply one-way hollow coreslabs to the buildings, without having any design changes and additionalcosts. So as to solve the above-mentioned problems, thus, there havebeen proposed bidirectional hollow core slabs using spherical or ovalplastic balls as hollow core bodies, which are invented by BubbleDeckcompany in Netherland and Cobiax company in Switzerland.

FIG. 1 shows a bidirectional hollow core slab of the prior art. Asshown, the bidirectional hollow core slab is configured by arrangingball-shaped hollow core bodies in rows and columns in such a manner asto be buried into concrete, so that the slab have bidirectionalresistance characteristics. As shown in FIG. 1, the bidirectional hollowcore slab is formed wherein a slab lower portion and a slab upperportion are connected unitarily to each other by means of concretefilled between the ball-shaped hollow core bodies, thereby providing thebidirectional structure to the slab. Under the above-mentionedbidirectional hollow core slab, special attention should be paid to thefixation of the positions of the hollow core bodies.

The hollow rate generated by the shape and volume of the hollow corebodies in the bidirectional hollow core slab determines the amount ofconcrete of the slab and the amount of reduction of the slab weight andfurther defines the structural performance of the slab. In other words,the higher the hollow rate is, the smaller the amount of concrete of theslab is. In this case, however, the structural resistance of the slabbecomes low. In case of the bidirectional hollow core slab, especially,the slab upper portion and the slab lower portion may be separated andmoved from each other, while placing the hollow core bodiestherebetween.

Therefore, there is a definite need for the development of a novelbidirectional hollow core slab capable of removing the reduction of thestructural performance caused by the increment of the hollow ratethereof and improving the constructability thereof.

SUMMARY OF INVENTION

Accordingly, the present invention has been made in view of theabove-mentioned problems occurring in the prior art, and it is an objectof the present invention to provide a hollow core body that has asubstantially high hollow rate and is used for a bidirectional hollowcore slab in a structurally stable state.

It is another object of the present invention to provide a bidirectionalhollow core slab that is formed by stably locating hollow core bodiesbetween upper and lower steel bars, thereby ensuring the quality ofconstruction in the structural design.

It is still another object of the present invention to provide aconstruction method of a bidirectional hollow core slab that is capableof simplifying the arrangement work of the steel bars.

To accomplish the above objects, according to an aspect of the presentinvention, there is provided a hollow core body that is adapted to beburied into concrete, having a generally doughnut-shaped outer casehaving a hollow portion formed on the center thereof.

To accomplish the above objects, according to another aspect of thepresent invention, there is provided a bidirectional hollow core slabthat is made by restraining doughnut-shaped hollow core bodies intosteel bar cages or into upper and lower steel bars, thereby stablylocating the doughnut-shaped hollow core bodies into slab concrete.

According to the present invention, the following advantages can beexpected.

Firstly, the hollow core slab with the bidirectional resistancecharacteristics can be constructed in a structurally stable state.Especially, the slab concrete is filled into the hollow portions of thedoughnut-shaped hollow core bodies, so that the unification of the upperand lower portions placing the hollow core bodies therebetween can beimproved to construct the structurally reinforced hollow core slab.

Secondly, the hollow core bodies are buried into the slab concrete inthe state of being restrained in the steel bar cages or the steel barspacers, so that they can be located on the center between the slabupper and lower steel bars to ensure the quality of construction, andmore particularly, the steel bar cages serve to fix the positions of thehollow core bodies as well as serve as shear steel bars in the state ofbeing restrained in the slab concrete, thereby constructing astructurally advantageous hollow core slab.

Lastly, the distributing bars of the upper and lower steel bars of thebidirectional hollow core slab can be in advance coupled to the steelbar cages or steel bar spacers for fixing the positions of the hollowcore bodies, thereby permitting the arrangement work of the slab steelbars to be simplified.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a bidirectional hollow core slab of the prior art.

FIGS. 2 and 3 show doughnut-shaped hollow core bodies according to thepresent invention.

FIG. 4 shows a bidirectional hollow core slab constructed by using thedoughnut-shaped hollow core body of FIG. 2.

FIGS. 5 to 7 show a steel bar cage formed of bent bars and thedoughnut-shaped hollow core body of FIG. 2 restrainedly mounted in thesteel bar cage.

FIGS. 8 and 9 show the process for constructing the bidirectional hollowcore slab using the steel bar cage of FIG. 7 and the section of thefinished bidirectional hollow core slab.

FIGS. 10 and 11 show a steel bar cage formed of horizontal bars and thedoughnut-shaped hollow core body of FIG. 2 restrainedly mounted in thesteel bar cage.

FIGS. 12 and 13 show the process for constructing the bidirectionalhollow core slab using the steel bar cage of FIG. 11 and the section ofthe finished bidirectional hollow core slab.

FIGS. 14 and 15 show steel bar spacers and the state where thedoughnut-shaped hollow core bodies of FIG. 3 are disposed using thesteel bar spacers.

FIG. 16 shows the section of the bidirectional hollow core slab made byusing the steel bar spacers of FIG. 14.

DETAILED DESCRIPTION OF EMBODIMENTS OF INVENTION

According to a first aspect of the present invention, there is provideda hollow core body that is adapted to be buried into concrete for theconstruction of a lightweight concrete member, having a hollow portionwith a circular section formed in the center thereof and corners roundedwith curved surfaces, thereby providing a generally doughnut-shapedouter case.

According to a second aspect of the present invention, there is provideda bidirectional hollow core slab including:

steel bar cages each having first and second side bent bars, an upperbent bar, and first and second end tilt bars; doughnut-shaped hollowcore bodies spacedly arranged in rows and columns in such a manner as tobe restrained in the steel bar cages by means of fitting slots formed onboth sides facing each other; slab lower steel bars arranged beneath thesteel bar cages; slab upper steel bars arranged on the steel bar cages;and slab concrete cast and cured to a thickness through which the slablower and upper steel bars are buried.

According to a third aspect of the present invention, there is provideda bidirectional hollow core slab including: steel bar cages having firstand second upper and lower horizontal bars, first and second side tiltbars, upper tilt bars, and first and second end tilt bars;doughnut-shaped hollow core bodies spacedly arranged in rows and columnsin such a manner as to be restrained in the steel bar cages by means offitting slots formed on both sides facing each other; slab lower steelbars arranged beneath the steel bar cages; slab upper steel barsarranged on the steel bar cages; and slab concrete cast and cured to athickness through which the slab lower and upper steel bars are buried.

According to a fourth aspect of the present invention, there is provideda bidirectional hollow core slab including: doughnut-shaped hollow corebodies spacedly arranged in rows and columns; slab lower steel barsarranged as main bars and distributing bars beneath the doughnut-shapedhollow core bodies; slab upper steel bars arranged as main bars anddistributing bars on the doughnut-shaped hollow core bodies; steel barspacers disposed and coupled between the doughnut-shaped hollow corebodies and the slab lower and upper steel bars; and slab concrete castand cured to a thickness through which the slab lower and upper steelbars are buried,

According to a fifth aspect of the present invention, there is provideda construction method of a bidirectional hollow core slab, including thesteps of: arranging slab lower steel bars; disposing steel bar cagesinto which doughnut-shaped hollow core bodies are restrained on the slablower steel bars; arranging slab upper steel bars on the steel barcages; and casting and curing slab concrete onto the slab lower andupper steel bars.

Hereinafter, an explanation on a doughnut-shaped hollow core body, abidirectional hollow core slab using the same, and a construction methodthereof according to the present invention will be given with referenceto the attached drawings.

FIGS. 2 and 3 show doughnut-shaped hollow core bodies according to thepresent invention.

A hollow core body 100 is buried into concrete so that the space inwhich the hollow core body 100 is disposed is not filled with theconcrete, thereby providing a lightweight concrete member. That is, thehollow core body 100 serves as a hollow core to give a light weight tothe concrete member.

According to the present invention, especially, the hollow core body 100has a hollow portion 110 formed on the center thereof, thereby having agenerally doughnut-shaped outer case. That is, the doughnut-shapedhollow core body according to the present invention is configuredwherein the hollow portion 110 with a circular section is formed in thecenter thereof and corners are rounded with curved surfaces, therebyproviding a generally doughnut-shaped outer case.

Further, the doughnut-shaped hollow core body 100 according to thepresent invention has a cavity area 120 formed into the doughnut-shapedouter case and two or more constitution parts 100 a and 100 b coupled toeach other. The cavity area 120 serves to further provide the lightweight to the doughnut-shaped hollow core body 100, and the couplingstructure of the constitution parts 100 a and 100 b enables theconstitution parts 100 a and 100 b to be laid on top of each other,thereby minimizing their volume while carried. The cavity area 120 maybe filled with an insulation material like Styrofoam and sound-proof andvibration-proof materials like rubber, and in this case, thedoughnut-shaped hollow core body 100 can be advantageously applied tothe places where the insulation and the vibration-proof resistance areneeded.

In the doughnut-shaped hollow core body 100, as shown in FIGS. 2 and 3,the two constitution parts 100 a and 100 b are coupled to each other,wherein in FIG. 2 they are coupled by means of stepped protrusions 131 aand 131 b formed to correspond to each other, and in FIG. 3 they arelocked by means of protruding pieces 132 a and locking members 132 bformed to correspond to each other.

On the other hand, it is checked from FIGS. 2 and 3 that fitting slots140 a, 140 b and 140 c are formed on the outer case of thedoughnut-shaped hollow core body 100. The fitting slots 140 a, 140 b and140 c are provided to restrain the doughnut-shaped hollow core body 100into a steel bar cage 200 or a steel bar spacer 300. Especially, thedoughnut-shaped hollow core body 100 of FIG. 3 has the X-shaped fittingslots 140 a formed on the sides thereof and straight line-shaped fittingslots 140 b and trapezoidal fitting slots 140 c formed on the top andunderside surfaces thereof, which enables the doughnut-shaped hollowcore body 100 to be utilized commercially irrespective of the kinds ofthe steel bar cage 200 and the steel bar spacer 300.

The doughnut-shaped hollow core body 100 can be made with a weight lowerthan the concrete when they have the same volume as each other, and whenit is considered that concrete is not recyclable, desirably, theconcrete can be replaced with the hollow core body 100 made of aneco-friendly material. For example, the hollow core body 100 is made ofeco-friendly bio plastic such as biodegradable plastic, biomass plasticand so on. The biomass plastic is a polymer made with recyclable organicresources (PLA and natural fiber) as a raw material, thereby inducingthe reduction of the amount of fossil resources to be used. So, anamount of CO₂ can be decreased by the amount of biomass replaced.Further, the hollow core body 100 may be made of plastic (PP, PE, etc.),and especially, if it is made of reinforced plastic to which about 40%glass fiber GF is added, the strength (tension and compression) of thehollow core body can be increased by about 2 to 3 times.

The hollow core body 100 for constructing the bidirectional hollow coreslab desirably has a height H in a range between 120 mm and 150 mm,lengths L1 and L2 in a range between 90 mm and 270 mm, and a diameter Dof the hollow portion 110 thereof in a range between 15 mm and 45 mm.The height H of the hollow core body 100 is obtained in consideration ofthe thickness of the hollow core slab and the covering thickness ofupper and lower steel bars of the hollow core slab, the lengths L1 andL2 thereof are obtained in consideration of the hollow rate (more than30%) of the hollow core slab, and the diameter D is obtained inconsideration of the compactibility of slab concrete and the hollow rateof the hollow core slab.

FIG. 4 shows a bidirectional hollow core slab constructed by using thedoughnut-shaped hollow core body of FIG. 2. The bidirectional hollowcore slab is made by spacedly arranging the doughnut-shaped hollow corebodies 100 in rows and columns in a form of a matrix between upper andlower steel bars 411, 412, 413 and 414 and by burying the hollow corebodies 100 into slab concrete 420.

More particularly, the slab concrete 420 is filled in the hollowportions 110 of the hollow core bodies 100, and thus, the concreteportions are formed at a given interval irrespective of the sizes of thehollow core body 100, thereby enabling the bidirectional hollow coreslab to be constructed in a structurally stable manner. That is, theslab lower portion into which the lower steel bars 411 and 412 areburied and the slab upper portion into which the upper steel bars 413and 414 are buried are connected unitarily to each other by means of theconcrete portions filled between the neighboring hollow core bodies 100and filled into the hollow portions 110 of the hollow core bodies 100,thereby strengthening the stability of the hollow core slab. As aanalysis result, it is found that concrete is filled into the hollowportions 110, thereby increasing the strength of the hollow core slaband decreasing the deflection of the hollow core slab, and further, itis found that the corners of the hollow core bodies 100 are rounded todistribute the cracks of the concrete and to delay the breakage thereof.

On the other hand, it is important to fix the positions of the hollowcore bodies 100 in the construction of the bidirectional hollow coreslab. According to the present invention, there are two methods forfixing the positions of the hollow core bodies 100 through steel barcages 200 and through steel bar spacers 300. FIGS. 5 to 13 show themethod for fixing the positions of the hollow core bodies 100 throughthe steel bar cages 200, and FIGS. 14 to 16 show the method for fixingthe positions of the hollow core bodies 100 through the steel barspacers 300. The steel bar cages 200 and the steel bar spacers 300control the mobility of the hollow core bodies 100, thereby allowingthem to be stably positioned between the upper and lower steel bars 411,412, 413 and 414.

Each steel bar cage 200 adapted to fix the position of the hollow corebody 100, as shown in FIGS. 5 to 13, is made by connecting steel bars(or steel wires, or materials equivalent to the steel bars) andconfigured to restrain and mount the hollow core body 100 thereinto.After the steel bar cages 200 are buried into the slab concrete 420,they are restrained by the slab concrete 420 to supplement the reductionof the shear performance caused by the loss of the section through thehollow core body 100.

FIGS. 5 to 7 show steel bar cages formed of bent bars and thedoughnut-shaped hollow core body of FIG. 2 restrainedly mounted in thesteel bar cage. The steel bar cage 200 of FIG. 5 has a basic structurein which one hollow core body 100 is restrainedly mounted. The steel barcage 200 of FIG. 6 has a structure wherein the steel bar cage of FIG. 5is extended by two times to restrain and mount two hollow core bodies100 thereinto. The steel bar cage 200 of FIG. 7 has a structure whereinthe steel bar cage of FIG. 5 is extended by four times to restrain andmount four hollow core bodies 100 thereinto. Of course, the steel barcage 200 can be extended to various lengths from that of FIG. 5.

The steel bar cage of FIG. 5 is made by coupling first and second sidebent bars 210 and 220, an upper bent bar 230, and first and second endtilt bars 241 and 242 by means of welding. The first side bent bar 210is bent and divided into a first inclined portion 211 and firsthorizontal portions 212 formed on both sides of the first inclinedportion 211, in such a manner as to be inclinedly erected to form thefirst side of the steel bar cage 200. The second side bent bar 220 isbent and divided into a second inclined portion 221 and secondhorizontal portions 222 formed on both sides of the second inclinedportion 221 in such a manner as to be inclinedly erected toward thefirst side bent bar 210, while facing the first side bent bar 210,thereby forming the second side of the steel bar cage 200. Further, thesecond inclined portion 221 is located in a direction crossing the firstinclined portion 211 of the first side bent bar 210. The upper bent bar230 is bent and divided into a third inclined portion 231 and thirdhorizontal portions 232 formed on both sides of the third inclinedportion 231 in such a manner as to be horizontally located on the upperportion between the first and second side bent bars 210 and 220 facingeach other, thereby forming the upper side of the steel bar cage 200.Further, the third horizontal portions 232 are connected rigidly to thefirst and second horizontal portions 212 and 222 of the first and secondside bent bars 210 and 220. The first end tilt bar 241 is located toinclinedly connect the first horizontal portion 212 on one end of thefirst side bent bar 210 to the second horizontal portion 222 on one endof the second side bent bar 220. The second end tilt bar 242 is locatedto inclinedly connect the first horizontal portion 212 on the other endof the first side bent bar 210 to the second horizontal portion 222 onthe other end of the second side bent bar 220.

The steel bar cages 200 of FIGS. 6 and 7 have the structures wherein thesteel bar cage of FIG. 5 is extended in such a manner as to becontinuously bent to a trapezoidal shape for the first and second sidebent bars 210 and 220 and the upper bent bar 230. That is, the steel barcage 200 of FIG. 6 is made by coupling the first and second side bentbars 210 and 220 and the upper bent bar 230 having two first, second andthird inclined portions 211, 221 and 231 and the first, second and thirdhorizontal portions 212, 222 and 232 at both ends thereof. The steel barcage 200 of FIG. 7 is made by coupling the first and second side bentbars 210 and 220 and the upper bent bar 230 having four first, secondand third inclined portions 211, 221 and 231 and the first, second andthird horizontal portions 212, 222 and 232 at both ends thereof. Thesteel bar cage 200 of FIG. 7 has a desirable size applicable to theconstruction site when considering all conditions inclusive ofconveyance and work site.

The steel bar cages 200 of FIGS. 5 to 7 have the whole outer shape of ahexahedron, and thus, they can be erected by themselves. That is, thefirst and second side bent bars 210 and 220 constitute both sides of thehexahedron, the upper bent bar 230 an upper side thereof, and the firstand second tilt bent bars 241 and 242 front and rear sides thereof, andthen the first and second horizontal portions 212 and 222 of the firstand second side bent bars 210 and 220 become the support points of thehexahedron, thereby making the steel bar cage 200 erected by itself.Especially, the first and second side bent bars 210 and 220 are inclinedtoward each other, so that the front and rear sides of the steel barcage 200 have the trapezoidal shapes (see FIGS. 5 b, 6 b and 7 b).

It is checked from FIGS. 5 c, 6 c and 7 c that the doughnut-shapedhollow core body 100 of FIG. 2 is restrainedly mounted into the steelbar cage 200. So as to restrainedly mount the hollow core body 100 intothe steel bar cage 200, the hollow core body 100 should have the fittingslots 140 a formed on both sides facing each other. In this case, if thehollow core body 100 is inserted into the steel bar cage 200, the firstand second inclined portions 211 and 221 of the first and second sidebent bars 210 and 220 are insertedly fitted to the fitting slots 140 ato permit the hollow core body 100 to be restrained into the steel barcage 200. After the hollow core body 100 has been restrained into thesteel bar cage 200, even if a given buoyancy is applied to the hollowcore body 100 while the slab concrete 420 is being cast, the hollow corebody 100 is locked to the first and second side bent bars 210 and 220inclined toward each other and the floating of the hollow core body 100is thus suppressed. As a result, the hollow core body 100 is stablyburied at a given position into the slab concrete 420. When consideringthe construction state of the hollow core body 100, generally, aplurality of hollow core bodies 100 are restrained into one steel barcage 200, as shown in FIG. 6 and FIG. 7, and in this case, thearrangement intervals of the plurality of hollow core bodies 100 can beadjusted by means of the lengths of the first, second and thirdhorizontal portions 212, 222 and 232 located in the middle of the firstand second side bent bars 210 and 220 and the upper bent bar 230.

On the other hand, the hollow core body 100 of FIG. 2 has both sidefitting slots 140 a formed in the same arrangements of the first andsecond inclined portions 211 and 221 of the first and second side bentbars 210 and 220, and the hollow core body 100 of FIG. 3 has both sidefitting slots 140 a formed to a shape of ‘X’ crossing the arrangementsof the first and second inclined portions 211 and 221 of the first andsecond side bent bars 210 and 220. In this case, the hollow core body100 of FIG. 3 is more advantageous than the hollow core body 100 of FIG.2 because it has no limitation in the direction of the installation. Inmore detail, in case of the hollow core body 100 of FIG. 2, thedirections of the fitting slots 140 a formed should correspond to thedirections of the first and second inclined portions 211 and 221 of thefirst and second side bent bars 210 and 220, and contrarily, in case ofthe hollow core body 100 of FIG. 3, the directions of the first andsecond inclined portions 211 and 221 of the first and second side bentbars 210 and 220 correspond to the directions of the fitting slots 140 aformed on both sides of the hollow core body 100, which has nolimitation in the direction of installation.

FIGS. 8 and 9 show the process for constructing the bidirectional hollowcore slab using the steel bar cage of FIG. 7 and the section of thefinished bidirectional hollow core slab. In this case, the same processis applied to the steel bar cages 200 as shown in FIGS. 5 and 6. Thebidirectional hollow core slab is constructed first by crossedlyarranging main bars 411 and distributing bars 412 as the lower steelbars, disposing the steel bar cages 200 into which the doughnut-shapedhollow core bodies 100 are restrained on the lower steel bars 411 and412, crossedly arranging distributing bars 413 and main bars 414 as theupper steel bars on the steel bar cages 200, and casting and curing theslab concrete 420 thereon. At this time, the steel bar cages 200 aretied by means of a binding wire in such a manner as to be fixed to thelower steel bars 411 and 412. On the other hand, the steel bar cages 200serve as spacers for constantly maintaining the arrangement positions ofthe upper steel bars 413 and 414.

FIGS. 10 and 11 show a steel bar cage formed of horizontal bars, whereinthe steel bar cage is made with the distributing bars of the upper andlower steel bars of the slab.

The steel bar cage of FIG. 10 is made by coupling first and second upperand lower horizontal bars 251, 252, 253 and 254, first and second sidetilt bars 261 and 262, upper tilt bars 263, and first and second endtilt bars 241 and 242 by means of welding. The first and second lowerhorizontal bars 251 and 252 are spaced apart from each other in parallelwith each other, and above the first and second lower horizontal bars251 and 252, the first and second upper horizontal bars 253 and 254 arespaced apart from each other with a width smaller than the first andsecond lower horizontal bars 251 and 252. Accordingly, the first andsecond upper and lower horizontal bars 251, 252, 253 and 254 have atrapezoidal arrangement structure. The first side tilt bars 261 connectthe first upper and lower horizontal bars 251 and 253 to each other,while being inclined to each other along the lengthwise directions ofthe first upper and lower horizontal bars 251 and 253, and in this case,the inclined directions of the neighboring first side tilt bars 261 areopposite to each other. The second side tilt bars 262 connect the secondupper and lower horizontal bars 252 and 254 to each other, while beinginclined to each other along the lengthwise directions of the secondupper and lower horizontal bars 252 and 254, and in this case, theinclined directions of the second side tilt bars 262 are opposite tothose of the first side tilt bars 261 in such a manner as to cross thefirst side tilt bars 261. The upper tilt bars 263 connect the first andsecond upper horizontal bars 253 and 254 to each other, while beinginclined to each other along the lengthwise directions of the first andsecond upper horizontal bars 253 and 254, and thus, they connect thefirst and second side tilt bars 261 and 262 facing each other. The firstend tilt bar 241 inclinedly connects one end portion of the first upperhorizontal bar 253 and one end portion of the second lower horizontalbar 252, and the second end tilt bar 242 inclinedly connects the otherend portion of the first upper horizontal bar 253 and the other endportion of the second lower horizontal bar 252, or inclinedly connectsthe other end portion of the second upper horizontal bar 254 and theother end portion of the first lower horizontal bar 251. In the steelbar cage 200 as shown in FIG. 10, the first and second upper and lowerhorizontal bars 251, 252, 253 and 254 are used as the distributing bars412 and 413 of the upper and lower steel bars of the slab.

The steel bar cage 200 as shown in FIG. 10 has the whole outerappearance similar to the steel bar cages 200 as shown in FIGS. 5 to 7.The first and second upper and lower horizontal bars 251, 252, 253 and254 correspond to the first, second and third horizontal portions 212,222 and 232 of the first and second side bent bars 210 and 220 and theupper bent bar 230, the first and second side tilt bars 261 and 263correspond to the first and second inclined portions 211 and 221 of thefirst and second side bent bars 210 and 220, and the upper tilt bars 263have the same arrangements as the third inclined portion 231 of theupper bent bar 230. Accordingly, the hollow core bodies 100 arerestrained in the steel bar cage 200 as shown in FIG. 10, in the samemanner as the steel bar cages 200 as shown in FIGS. 5 to 7.

The steel bar cage 200 as shown in FIG. 11 is made by welding the firstand second upper and lower horizontal bars 251, 252, 253 and 254 to thesteel bar cage 200 as shown in FIG. 7. That is, the first horizontalbars 212 located at the lower portions of the first side bent bars 210are connected to each other by means of the first lower horizontal bar251, the second horizontal bars 222 located at the lower portions of thesecond side bent bars 220 are connected to each other by means of thesecond lower horizontal bar 252, the connected portions between thefirst horizontal bars 212 located at the upper portions of the firstside bent bars 210 and the third horizontal bars 232 located at onesides of the upper bent bars 230 are connected to each other by means ofthe first upper horizontal bar 253, and the connected portions betweenthe second horizontal bars 222 located at the upper portions of thesecond side bent bars 220 and the third horizontal bars 232 located atthe other sides of the upper bent bars 230 are connected to each otherby means of the second upper horizontal bar 254. Since the first andsecond upper and lower horizontal bars 251, 252, 253 and 254 are used asthe distributing bars 412 and 413 of the upper and lower steel bars ofthe slab, the steel bar cage 200 as shown in FIG. 11 is made by inadvance welding the distributing bars 412 and 413 of the upper and lowersteel bars of the slab to the steel bar cage 200 as shown in FIG. 7.

In case of the steel bar cage 200 formed of the horizontal bars as shownin FIGS. 10 and 11, desirably, both ends of each of the first and secondupper and lower horizontal bars 251, 252, 253 and 254 are more extendedthan the other portions, and the extended one ends are bent. As aresult, when the steel bar cages 200 are continuously arranged serially,the first and second upper and lower horizontal bars 251, 252, 253 and254 can be connected to the neighboring first and second upper and lowerhorizontal bars 251, 252, 253 and 254.

FIGS. 12 and 13 show the process for constructing the bidirectionalhollow core slab using the steel bar cage of FIGS. 11 a to 11 c and thesection of the finished bidirectional hollow core slab, and in thiscase, the same process is applied to the steel bar cage 200 as shown inFIG. 10. The steel bar cage 200 as shown in FIG. 11 is made by weldingthe first and second upper and lower horizontal bars 251, 252, 253 and254 to the steel bar cage 200 as shown in FIG. 7, so that if the steelbar cage 200 as shown in FIG. 11 is used, the process of arranging thedistributing bars 412 and 413 in the arrangements of the upper and lowersteel bars of the slab can be avoided.

Steel bar spacers 300 as shown in FIGS. 14 to 16, which are adapted tofix the positions of the hollow core bodies 100, are configured to becoupled to the hollow core bodies 100 and the distributing bars 312 and413, while being located between the hollow core bodies 100 and thedistributing bars 312 and 413. In more detail, each steel bar spacer 300includes a steel bar coupling piece 310 formed to be welded or fitted tothe distributing bars 412 and 413 and a protrusion 320 formed to befitted to the hollow core body 100.

FIG. 14 show the example of the steel bar spacers 300 made of steelbars. The steel bar spacers 300 as shown in FIG. 14 are formed bycontinuously bending the steel bar to form the ∩-shaped protrusions 320at the center portions and the horizontal steel bar coupling pieces 310at both ends thereof in such a manner as to be welded to thedistributing bars 412 and 413.

FIG. 15 show the example of the steel bar spacers 300 made by means ofplastic injection molding. The steel bar spacers 300 as shown in FIG.15, which are used in the conventional practice, are formed of the steelbar coupling pieces 310 open by elasticity and the elastic protrusions320 of a trapezoidal shape formed on the lower portion of the steel barcoupling pieces 310, so that the distributing bars 412 and 413 arefitted to the steel bar coupling pieces 310.

It is appreciated from FIGS. 14 b and 15 b that the doughnut-shapedhollow core bodies 100 of FIG. 3 are coupled to the steel bar spacers300. So as to couple the hollow core bodies 100 to the steel bar spacers300, each hollow core body 100 should have the fitting slots 140 b and140 c formed on the top and underside surfaces thereof, and at thistime, the fitting slots 140 b and 140 c should have the correspondingshape to the protrusions 320 of the steel bar spacers 300, so that whenthe hollow core bodies 100 are coupled to the steel bar spacers 300, theprotrusions 320 are fitted to the fitting slots 140 b and 140 c, therebyachieving the coupling. After the hollow core bodies 100 have beencoupled to the steel bar spacers 300, even if a given buoyancy isapplied to the hollow core bodies 100 while the slab concrete 420 isbeing cast, the floating of the hollow core bodies 100 is suppressed bythe weight of the upper distributing bars 413 coupled to the steel barcoupling pieces 310 of the steel bar spacers 300, and thus, the hollowcore bodies 100 are stably buried at a given position into the slabconcrete 420. The bidirectional hollow core slab made by using the steelbar spacers 300 is shown in FIG. 16.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by theembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

1. A hollow core body 100, which is adapted to be buried into concretefor the construction of a lightweight concrete member, having a hollowportion 110 with a circular section formed in the center thereof andcorners rounded with curved surfaces, thereby providing a generallydoughnut-shaped outer case.
 2. The hollow core body as defined in claim1, wherein a cavity area 120 is formed in the doughnut-shaped outercase.
 3. The hollow core body as defined in claim 2, wherein the cavityarea 120 is filled with an insulation material or a vibration-proofmaterial.
 4. The hollow core body as defined in claim 2, wherein two ormore constitution parts 100 a and 100 b are coupled to each other toform the hollow core body 100, each of the constitution parts 100 a and100 b being made of any one of reinforced plastic into which glass fiberis mixed, biodegradable plastic, and biomass plastic.
 5. The hollow corebody as defined in claim 1, wherein a height H of the hollow core body100 is in a range between 120 mm and 150 mm, lengths L1 and L2 thereofin a range between 90 mm and 270 mm, and a diameter D of the hollowportion 110 thereof in a range between 15 mm and 45 mm.
 6. Abidirectional hollow core slab comprising: steel bar cages 200 made bycoupling steel bars; doughnut-shaped hollow core bodies 100 spacedlyarranged in rows and columns in such a manner as to be restrained in thesteel bar cages 200; slab lower steel bars 411 and 412 crossedlyarranged as main bars and distributing bars beneath the steel bar cages200; slab upper steel bars 413 and 414 crossedly arranged as main barsand distributing bars on the steel bar cages 200; and slab concrete 420cast and cured to a thickness through which the slab lower and uppersteel bars 411, 412, 413 and 414 are buried, wherein each steel bar cage200 comprises: a first side bent bar 210 bent and divided into a firstinclined portion 211 and first horizontal portions 212 formed on bothsides of the first inclined portion 211, the first side bent bar 210being inclinedly erected to form the first side thereof; a second sidebent bar 220 bent and divided into a second inclined portion 221 andsecond horizontal portions 222 formed on both sides of the secondinclined portion 221, the second side bent bar 220 being inclinedlyerected toward the first side bent bar 210 in such a manner as to facethe first side bent bar 210, thereby forming the second side thereof,and the second inclined portion 221 being located in a directioncrossing the first inclined portion 211 of the first side bent bar 210;an upper bent bar 230 bent and divided into a third inclined portion 231and third horizontal portions 232 formed on both sides of the thirdinclined portion 231, the upper bent bar 230 being horizontally locatedon the upper portion between the first and second side bent bars 210 and220 facing each other, thereby forming the upper side thereof, and thethird horizontal portions 232 being connected to the first and secondhorizontal portions 212 and 222 of the first and second side bent bars210 and 220; a first end tilt bar 241 located to inclinedly connect thefirst horizontal portion 212 on one end of the first side bent bar 12101to the second horizontal portion 222 on one end of the second side bentbar 220; and a second end tilt bar 242 located to inclinedly connect thefirst horizontal portion 212 on the other end of the first side bent bar210 to the second horizontal portion 222 on the other end of the secondside bent bar 220, and each doughnut-shaped hollow core body 100comprises fitting slots 140 a formed correspondingly on both sidesfacing each other, into which the first and second inclined portions 211and 221 of the first and second side bent bars 210 and 220 areinsertedly fitted, so that the hollow core bodies 100 are inserted intothe steel bar cages 200 and the first and second inclined portions 211and 221 of the first and second side bent bars 210 and 220 areinsertedly fitted to the fitting slots 140 a, thereby being restrainedinto the steel bar cages
 200. 7. The bidirectional hollow core slab asdefined in claim 6, wherein the first and second side bent bars 210 and220 and the upper bent bar 230 of each steel bar cage 200 arecontinuously bent to a trapezoidal shape to provide two or more first,second and third inclined portions 211, 221 and 231, thereby forming thefirst, second and third horizontal portions 212, 222 and 232 at bothends of the respective inclined portions, and each steel bar cage 200has the plurality of doughnut-shaped hollow core bodies 100 restrainedlyinserted thereinto.
 8. A bidirectional hollow core slab comprising:steel bar cages 200 made by coupling steel bars; doughnut-shaped hollowcore bodies 100 spacedly arranged in rows and columns in such a manneras to be restrained in the steel bar cages 200; slab lower steel bars411 arranged as main bars beneath the steel bar cages 200; slab uppersteel bars 414 arranged as main bars on the steel bar cages 200 in adirection parallel to the slab lower steel bars 411; and slab concrete420 cast and cured to a thickness through which the slab lower and uppersteel bars 411 and 414 are buried, wherein each steel bar cage 200comprises: first and second lower horizontal bars 251 and 252 spacedapart from each other in parallel with each other; first and secondupper horizontal bars 253 and 254 spaced apart from each other with awidth smaller than the first and second lower horizontal bars 251 and252 above the first and second lower horizontal bars 251 and 252; afirst side tilt bars 261 adapted to connect the first upper and lowerhorizontal bars 251 and 253 to each other, while being inclined to eachother along the lengthwise directions of the first upper and lowerhorizontal bars 251 and 253 in such a manner where the inclineddirections of the neighboring first side tilt bars 261 are opposite toeach other; second side tilt bars 262 adapted to connect the secondupper and lower horizontal bars 252 and 254 to each other, while beinginclined to each other along the lengthwise directions of the secondupper and lower horizontal bars 252 and 254 in such a manner where theinclined directions of the second side tilt bars 262 are opposite tothose of those of the first side tilt bars 261 in such a manner as tocross the first side tilt bars 261; upper tilt bars 263 adapted toconnect the first and second upper horizontal bars 253 and 254 to eachother, while being inclined to each other along the lengthwisedirections of the first and second upper horizontal bars 253 and 254 insuch a manner as to connect the first and second side tilt bars 261 and262 facing each other; a first end tilt bar 241 adapted to inclinedlyconnect one end portion of the first upper horizontal bar 253 and oneend portion of the second lower horizontal bar 252; and a second endtilt bar 242 adapted to inclinedly connect the other end portion of thefirst upper horizontal bar 253 and the other end portion of the secondlower horizontal bar 252 or to inclinedly connect the other end portionof the second upper horizontal bar 254 and the other end portion of thefirst lower horizontal bar 251, and each doughnut-shaped hollow corebody 100 comprises fitting slots 140 a formed correspondingly on bothsides facing each other, into which the first and second side tilt bars261 and 262 are insertedly fitted, so that the hollow core bodies 100are inserted into the steel bar cages 200 and the first and second sidetilt bars 261 and 262 are insertedly fitted to the fitting slots 140 a,thereby being restrained into the steel bar cages
 200. 9. Thebidirectional hollow core slab as defined in claim 6, wherein thefitting slots 140 a of each doughnut-shaped hollow core body 100 areformed in a shape of X corresponding to the arrangements of the firstand second inclined portions 211 and 221 of the first and second sidebent bars 210 and 220 or corresponding to the arrangement of the firstand second side tilt bars 261 and
 262. 10. A bidirectional hollow coreslab comprising: doughnut-shaped hollow core bodies 100 spacedlyarranged in rows and columns; slab lower steel bars 411 and 412 arrangedas main bars and distributing bars beneath the doughnut-shaped hollowcore bodies 100; slab upper steel bars 413 and 414 arranged as main barsand distributing bars on the doughnut-shaped hollow core bodies 100;steel bar spacers 300 disposed between the doughnut-shaped hollow corebodies 100 and the distributing bars 412 and 413 of the slab lower andupper steel bars; and slab concrete 420 cast and cured to a thicknessthrough which the slab lower and upper steel bars 411, 412, 413 and 414are buried, wherein each steel bar spacer 300 comprises: a steel barcoupling piece 310 formed to be welded or fitted to the distributingbars 412 and 413; and a protrusion 320 formed to be fitted to eachdoughnut-shaped hollow core body 100, and each doughnut-shaped hollowcore body 100 comprises fitting slots 140 b and 140 c formed on the topand underside surfaces facing each other, so that the protrusions 320 ofthe steel bar spacers 300 are fitted to the fitting slots 140 b and 140c, thereby being restrained into the distributing bars 412 and
 413. 11.A construction method of a bidirectional hollow core slab as defined inclaim 6, comprising the steps of: crossedly arranging main bars 411 anddistributing bars 412 as slab lower steel bars; disposing steel barcages 200 into which doughnut-shaped hollow core bodies 100 arerestrained on the main bars 411 of the slab lower steel bars; crossedlyarranging distributing bars 413 and main bars 414 as slab upper steelbars on the steel bar cages 200; and casting and curing slab concrete420 onto the slab lower and upper steel bars.
 12. A construction methodof a bidirectional hollow core slab as defined in claim 8, comprisingthe steps of: crossedly arranging main bars 411 as slab lower steelbars; disposing steel bar cages 200 into which doughnut-shaped hollowcore bodies 100 are restrained on the main bars 411 of the slab lowersteel bars, while first and second lower horizontal bars 251 and 252 ofthe steel bar cages 200 are being arranged to cross the main bars 411 ofthe slab lower steel bars; arranging main bars 414 as slab upper steelbars on the steel bar cages 200, while the main bars 414 of the slabupper steel bars are being arranged to cross first and second upperhorizontal bars 253 and 254 of the steel bar cages 200; and casting andcuring slab concrete 420 onto the slab lower and upper steel bars. 13.The hollow core body as defined in claim 2, wherein a height H of thehollow core body (100) is in a range between 120 mm and 150 mm, lengthsL1 and L2 thereof in a range between 90 mm and 270 mm, and a diameter Dof the hollow portion (110) thereof in a range between 15 mm and 45 mm.14. The hollow core body as defined in claim 3, wherein a height H ofthe hollow core body (100) is in a range between 120 mm and 150 mm,lengths L1 and L2 thereof in a range between 90 mm and 270 mm, and adiameter D of the hollow portion (110) thereof in a range between 15 mmand 45 mm.
 15. The hollow core body as defined in claim 4, wherein aheight H of the hollow core body (100) is in a range between 120 mm and150 mm, lengths L1 and L2 thereof in a range between 90 mm and 270 mm,and a diameter D of the hollow portion (110) thereof in a range between15 mm and 45 mm.
 16. The bidirectional hollow core slab as defined inclaim 7, wherein the fitting slots (140 a) of each doughnut-shapedhollow core body (100) are formed in a shape of X corresponding to thearrangements of the first and second inclined portions (211) and (221)of the first and second side bent bars (210) and (220) or correspondingto the arrangement of the first and second side tilt bars (261) and(262).
 17. The bidirectional hollow core slab as defined in claim 8,wherein the fitting slots (140 a) of each doughnut-shaped hollow corebody (100) are formed in a shape of X corresponding to the arrangementsof the first and second inclined portions (211) and (221) of the firstand second side bent bars (210) and (220) or corresponding to thearrangement of the first and second side tilt bars (261) and (262). 18.A construction method of a bidirectional hollow core slab as defined inclaim 7, comprising the steps of: crossedly arranging main bars (411)and distributing bars (412 as slab lower steel bars; disposing steel barcages (200) into which doughnut-shaped hollow core bodies (100) arerestrained on the main bars (411) of the slab lower steel bars;crossedly arranging distributing bars (413) and main bars (414) as slabupper steel bars on the steel bar cages (200); and casting and curingslab concrete (420) onto the slab lower and upper steel bars.